1. Field of the Invention
The present invention is generally related to a mounting system for a marine propulsion device and, more particularly, to a mounting system that exhibits two different degrees of stiffness in response to different ranges of force magnitude imposed on the system.
2. Description of the Prior Art
Many different types of mounting systems are well known to those skilled in the art. Typically, a mounting system which is intended to isolate vibration and prevent it from being transmitted along a structure comprises an elastomeric material, such as rubber, in combination with inelastic materials, such as metal or hard polymer materials.
U.S. Pat. No. 5,242,146, which issued to Tecco et al on Sep. 7, 1993, describes an engine mount having an improved vibration isolation capability. The mount is intended for the purpose of mounting an automotive vehicle engine to the automotive vehicle chassis. The mount comprises a vibration isolator portion which is designed with relatively low stiffness to provide increased vibration isolation. Excessive displacements are avoided by snubbers. Snubbing action in one direction is provided by a circular snubber that is disposed in spaced relation to the vibration isolator portion. Snubbing action in other directions is provided by the particular design of the vibration isolator portion. Embodiments of both a front and a rear engine mount are provided.
U.S. Pat. No. 5,172,894, which issued to Hein et al on Dec. 22, 1992, describes a dual elastomeric/fluid engine mount. The engine mount is described as having two concentrically disposed annular resilient rubber springs, the outermost of which is provided with a pair of cavities and connecting passageway for receiving a dampening fluid. The spring rates of the two rubber springs can be individually tuned by the use of voids or cavities. Thus, there is a threefold manner in which the spring rate of the engine mount can be tuned.
U.S. Pat. No. 5,044,598, which issued to Mann et al on Sep. 3, 1991, describes a resilient motor mounting structure. The motor mount is suitable for use as a vibrational isolating motor mount. The mount connects the motor to a support structure by using a support fixture and a motor stud separated by a flexible member. A plurality of portions of the flexible member surround the support fixture and motor stud to lessen vibrational transfer from the motor to the structure fixture and to lessen metal fatigue caused by metal to metal contact.
U.S. Pat. No. 3,770,232, which issued to Blake on Nov. 6, 1973, describes a shock and vibration isolation mount. The mount includes a resilient elastomeric portion coupled in shock attenuating series with a stacked plurality of dished, disc-shaped annular metal springs. Normal low level vibration is attenuated by the resilient elastomeric portion acting alone, whereas high intensity shocks of sufficient magnitude to compress the resilient elastomeric portion to a substantially incompressible form of near infinite spring constant are continually attenuated by the stacked metal springs.
U.S. Pat. No. 6,419,534, which issued to Helsel et al on Jul. 16, 2002, discloses a structural support system for an outboard motor. The systems is provided for an outboard motor which uses four connectors attached to a support structure and to an engine system for isolating vibration from being transmitted to the marine vessel to which the outboard is attached. Each connector comprises an elastomeric portion for the purpose of isolating the vibration. Furthermore, the four connectors are disposed in a common plane which is generally perpendicular to a central axis of a driveshaft of the outboard motor. Although precise perpendicularity with the driveshaft axis is not required, it has been determined that if the plane extending through the connectors is within forty-five degrees of perpendicularity with the driveshaft axis, improved vibration isolation can be achieved. A support structure, or support saddle, completely surrounds the engine system in the plane of the connectors. All of the support of the outboard motor is provided by the connectors within the plane with no additional support provided at a lower position on the outboard motor driveshaft housing.
U.S. Pat. No. 6,123,620, which issued to Polakowski on Sep. 26, 2000, discloses a multirate coupler with improved vibration isolation capability. A coupler is provided which responds to relative rotation of a driving and a driver shaft with variable rates of stiffness. As the two shafts experience slight degrees of relative rotation, such as at idle speed, the elastically deformable member of the coupler responds in a relatively soft manner with a slight degree of stiffness. As relative rotation increases because of the transmission of higher torque between the driving and driven shafts, the elastically deformable member responds with a stiffer reaction. The elastically deformable member also reacts in a similar manner with differing rates of stiffness to misalignment of the driving and driven shafts.
U.S. Pat. No. 6,287,159, which issued to Polakowski et al on Sep. 11, 2001, discloses a marine propulsion device with a compliant isolation mounting system. A support apparatus for a marine propulsion system in a marine vessel is provided with a compliant member that is attachable to the transom of a marine vessel. In certain applications, the compliant member is directly attached to an intermediate plate and to an external frame member that is, in turn, attached directly to the transom of the marine vessel. The intermediate plate is attached directly to components of the marine propulsion system to provide support for the marine propulsion system relative to the transom, but while maintaining non-contact association between the marine propulsion and the transom.
U.S. Pat. No. 5,707,263, which issued to Eick et al on Jan. 13, 1998, discloses an adjustable trim position system. A system for a trimable marine stern drive shifts the trimable range on a conventional hydraulic trim system. The system includes an enlarged cylinder anchor pin hole in the drive shaft housing, an anchor pin smaller in size than the enlarged pin hole located in the in the drive shaft housing, and a movable trim adjustment insert that is inserted into the enlarged anchor pin hole to secure the anchor pin in a fixed position within the enlarged hole. It is preferred that the enlarged anchor pin hole be a substantially horizontal elongated hole, and that the trim adjustment insert be placed rearward of the anchor pin to position the anchor pin in a forward position, or forward of the anchor pin to locate the anchor pin in a rearward direction. The invention shifts the trimable range of the drive, while maintaining vibration isolation characteristics available in conventional hydraulic trim systems.
U.S. Pat. No. 6,309,264, which issued to Saito on Oct. 30, 2001, describes a cylinder assembly for a marine propulsion unit. An improved hydraulic cylinder arrangement for a marine propulsion unit permits primarily effective tilt and trim movement through a compound tilt and trim cylinder. At least one first shock absorber valve is provided on a tilt piston and at least one second shock absorber valve is provided on a tilt cylinder that acts as a trim piston in a trim adjusted range operation. In another feature of the invention, a filter is disposed upstream of the second shock absorber valve.
U.S. Pat. No. 6,280,268, which issued to Nishi et al on Aug. 28, 2001, describes a tilt device for a marine propulsion unit. A tilt device for a marine propulsion unit is disclosed where a shock blow valve comprises a disk valve fixed to a valve seat surface of the piston, the valve seat surface being provided with a seal member surrounding a communication hole which opens at the valve seat surface, and the disk valve is tightly connected to the seat member.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Various types of elastomeric mounting systems are well known to those skilled in the art. Marine stem drive systems are also well known to those skilled in the art. In addition, skilled artisans are aware of numerous types of hydraulic and piston cylinder combinations that can be used to move marine stem drive systems for the purpose of achieving desired trim and/or tilt positions.
In certain marine drive applications, a temporary impact is experienced during shifting procedures. As the transmission of the marine propulsion system is changed from neutral to forward or from neutral to reverse, an impact force is experienced as the drive system attempts to initiate movement of a stationary marine propeller. This impact can be sensed by the operator of a marine vessel because the shock forces are transmitted through the structure of the marine drive through the hydraulic cylinders used for trim and tilt, and into the transom of the marine vessel. Unfortunately, if soft resilient mounts are used to isolate this shock force, the steering and handling capabilities of the marine vessel can be severely and deleteriously affected. It would therefore by significantly beneficial if a system could be devised that isolates the shock forces associated with shifting while providing sufficient stiffness so as to avoid adverse effects on steering and handling of the marine vessel.
A marine propulsion system made in accordance with the preferred embodiment of the present invention comprises a marine drive unit, a hydraulic device attached to the marine drive unit and attachable to a marine vessel, and a vibration damping device attached between the marine drive unit and a first end of the hydraulic device. The hydraulic device has a first end attached to the drive unit and a second end which is attachable to the marine vessel. The vibration dampingdevice has a first rate of stiffness in response to a first magnitude of load and a second rate of stiffness in response to a second magnitude of load, whereas the second magnitude of load in greater than the first magnitude of load.
The vibration damping device comprises an outer tube, an inner tube, an elastomeric material disposed between the outer and inner tubes. The vibration damping device is attached to the first end of the hydraulic device. The outer tube is attached to the first end of the hydraulic device in a preferred embodiment, but the inner tube can also be attached to the first end of the hydraulic device in alternative embodiments.
The second rate of stiffness is greater than the first rate of stiffness and the first rate of stiffness is softer than the second rate of stiffness because of at least one cavity formed in the elastomeric material.
In a preferred embodiment, the outer tube is made of metal which can be stainless steel. Similarly, the inner tube is made of metal in a preferred embodiment and can be made of stainless steel. In one embodiment of the present invention, the inner tube is bonded to the elastomeric material and the outer tube is bonded to the elastomeric material. In an alternative embodiment, the elastomeric material is disposed in unbonded relation between the inner and outer tubes. Also, it should be understood that either one or both of the inner and outer tubes can be bonded to the elastomeric material or, alternatively, both the inner and outer tube can be unbonded to the elastomeric material.